Explained: What exactly is herd immunity

News: A recent serological survey in Delhi found the presence of coronavirus specific antibodies in about 23% of the samples tested.The results of the survey are being interpreted to suggest that Delhi could be approaching Herd immunity. However, scientists have cautioned against such conclusions.


  • What is Herd immunity? It is a stage of an epidemic in which some members of a population group remain protected from infection because a majority of those around them have already developed immunity either through vaccination or because they have been infected earlier.
  • What is a Serological Survey? It is a blood test that seeks to assess the prevalence of disease in a population by detecting the presence of specific antibodies against the virus.
    • The test only indicates past infections (which triggered an immune response) and is not used to detect active infections.
  • How was the survey conducted? The survey was conducted using IgG Enzyme-Linked Immunosorbent Assay(ELISA) test which has been approved by ICMR.

Additional Facts:

  • Antibodies: It is a protective protein produced by the immune system to fight external organisms like viruses that try to enter the body.These are produced only after the infection has happened and are specific to the attacking virus or bacterium.